Lieutenant General Ray Odiernotook over command of coalition forces in Iraq this week at a time when the "surge has succeeded" narrative has cemented the perception that American military tactics are the primary driver of events on the ground. But the reality confronting Gen Odierno could not be more different. A confident Nouri al-Maliki, the Iraqi prime minister, and other Iraqi actors are now firmly in control, leaving the scope of US military action severely limited. Despite the continued presence of nearly 140,000 US troops, America is not even the most influential foreign power in Iraq. Those troops are in fact an impediment to the political progress that must occur to secure a sustainable resolution to Iraq's numerous conflicts. The only responsible course of action for the next president is to drawdown US forces, increasing the stakes for Iraqi leaders and encouraging compromise rather than confrontation as they address their differences.

Maliki's transformation has been as swift as it was unexpected. Rescued from political extinction just 10 months ago, after the intervention of Condoleezza Rice prevented him from being voted out by his coalition partners, Maliki surprised most observers with an aggressive military push this spring to retake Basra from Shia militias, particularly Muqtada al-Sadr's Mahdi army. When that campaign faltered, Iran stepped in to save Maliki by pressuring Sadr to stand down both in the south and in Sadr City. Both bailouts have dramatically altered the landscape in Iraq. Maliki now appears to be doing Iran's bidding but relying on the crutch of American troops to back him up.

Maliki has consolidated his position and is increasing the power of the central government, directing Iraq's ever-growing military and intelligence apparatus independent of US control for the first time since the invasion. Emboldened by success in Basra and Sadr City, the Shia-dominated government in Baghdad is now projecting power into areas controlled by its ethnic and sectarian rivals. In the span of these short months the pendulum has swung entirely on the perceptions of Maliki, going from concerns about his alarming weakness to fears of dangerous over-confidence.

Last month, Maliki ordered the Iraqi army into the mostly Kurdish town of Khanaqin ostensibly as part of a broader military operation to root out al-Qaida militants in Diyala province. The move inflamed the Kurds, whose Peshmerga forces had kept out al-Qaida, and most viewed it as a naked power play by Baghdad. The standoff between the Kurdish Regional Government and Baghdad over Khanaqin has exacerbated Arab-Kurdish tensions and further imperiled any negotiated settlement in Kirkuk.

Next month, the central government will take over the Sunni Awakening Councils, the programme of US payments to Sunnis to turn against the insurgency that began in 2006 and is responsible for much of the reduction in violence. Maliki has pledged to integrate as many as 20,000 of these armed Sunni "sons of Iraq" into the security forces, but there are disturbing signs that the Shia government is orchestrating a campaign to harass, intimidate or arrest them, which could reignite Sunni-Shia conflict.

Iran is the ultimate beneficiary of these actions against the Kurds and the Sunnis. Tehran has its own Kurdish problem and does not want the Kurds in Iraq to establish firm control in the oil-rich areas beyond its current base in the three provinces in the north of Iraq. And, of course, the Shia mullahs have been in constant conflict with Iraq's Sunnis ever since they came to power in 1979, and have a vested interest in their continued marginalisation in post-Saddam Iraq. Even if these moves go bad it would serve Iranian interests, as Iraq would be weakened by spasms of violence, and it could prolong American involvement creating additional time for Iran to further develop its nuclear programme.

The cruel irony for Gen Odierno is that although American troops made vital contributions to the reduction in violence, there is nothing they can do to resolve these burgeoning conflicts, and the very stability that they provide is encouraging the various factions to aggressively advance their own objectives at the expense of necessary compromise which jeopardises these hard-fought gains.

Success in Iraq is now dependent upon increasing the incentives for Iraqi leaders toward accommodation. The best way to achieve this objective is to create an environment in which Iraqis are responsible for the full consequences of their actions. The large US troop presence is currently doing the opposite, embedding a moral hazard among Iraq's leaders and inhibiting consensus. The only way to preserve the gains of the last 18 months is to begin the orderly withdrawal of US troops.